The relationship between damage to tumor target cells and density of antigenic sites will be explored for antibody, T-cell and B-cell mediated mechanisms. A model system will utilize the azobenzenearsonate group towards which all three modes of reaction may be directed. The hapten will be coupled to target cells in varied density and cytotoxic effects by the three immunologic modes will be compared. This hapten probe will also be used to study turnover of various surface components on malignant cells. Efforts will be made to control the type of immune response directed to tumor-specific transplantation antigen by varying the mode of antigen presentation. Using an SV40 virus-induced tumor in mice, attempts will be made to determine whether surface alterations produced by conjugating hydrophobic groups to the tumor cells will produce primarily cell-mediated immunity upon inoculation.